1. Field of the Invention
The present invention relates generally to a genetic sequence encoding a polypeptide having methyltransferase activity and the use of the genetic sequence and/or the polypeptide to modify one or more phenotypic characteristics of a plant. More particularly, the methyltransferase of the present invention acts on flavonoids, preferably wherein the flavonoid is an anthocyanin. Even more particularly, the present invention relates to a polypeptide having S-adenosyl-L-methionine:anthocyanin 3′-O-methyltransferase or S-adenosyl-L-methionine:anthocyanin 3′,5′-O-methyltransferase activity. The present invention still further provides a genetic sequence encoding a polypeptide having methyltransferase activity derived from Petunia, Torenia, Fuchsia or Plumbago or botanically related plants. The instant invention further relates to antisense and sense molecules corresponding to all or part of the subject genetic sequence as well as genetically modified plants as well as cut flowers, parts, extracts and reproductive tissue from such plants.
2. Description of the Prior Art
Bibliographic details of the publications referred to by author in this specification are collected at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
The flower or ornamental plant industry strives to develop new and different varieties of flowers and/or plants. An effective way to create such novel varieties is through the manipulation of flower color. Classical breeding techniques have been used with some success to produce a wide range of colors for most of the commercial varieties of flowers and/or plants available today. This approach has been limited, however, by the constraints of a particular species' gene pool and for this reason it is rare for a single species to have the full spectrum of colored varieties. For example, the development of novel colored varieties of plants or plant parts such as flowers, foliage and stems would offer a significant opportunity in both the cut flower and ornamental markets. In the flower or ornamental plant industry, the development of novel colored varieties of major flowering species such as rose, chrysanthemum, tulip, lily, carnation, gerbera, orchid, lisianthus, begonia, torenia, geranium, petunia, nierembergia, pelargonium, impatiens and cyclamen would be of great interest. A more specific example would be the development of a blue rose or gerbera for the cut flower market.
In addition, the development of novel colored varieties of plant parts such as vegetables, fruits and seeds would offer significant opportunities in agriculture. For example, novel colored seeds would be useful as proprietary tags for plants. Furthermore modifications to flavonoids common to berries including grapes and their juices including wine have the potential to impart altered style characteristics of value to such fruit and byproduct industries.
Flower color is predominantly due to three types of pigment: flavonoids, carotenoids and betalains. Of the three, the flavonoids are the most common and contribute a range of colors from yellow to red to blue. The flavonoid molecules that make the major contribution to flower color are the anthocyanins, which are glycosylated derivatives of cyanidin and its methylated derivative peonidin, delphinidin and its methylated derivatives petunidin and malvidin and pelargonidin. Anthocyanins are localised in the vacuole of the epidermal cells of petals or vacuole of sub epidermal cells of leaves.
The flavonoid pigments are secondary metabolites of the phenylpropanoid pathway. The biosynthetic pathway for the flavonoid pigments (flavonoid pathway) is well established, (Holton and Cornish, Plant Cell 7: 1071-1083, 1995; Mol et al., Trends Plant Sci. 3: 212-217, 1998; Winkel-Shirley, Plant Physiol. 126: 485-493, 2001a and Winkel-Shirley, Plant Physiol. 127: 1399-1404, 2001b) and is shown in FIGS. 1A and B. Three reactions and enzymes are involved in the conversion of phenylalanine to p-coumaryl-CoA, one of the first key substrates in the flavonoid pathway. The enzymes are phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H) and 4-coumarate:CoA ligase (4CL). The first committed step in the pathway involves the condensation of three molecules of malonyl-CoA (provided by the action of acetyl CoA carboxylase (ACC) on acetyl CoA and CO2) with one molecule of p-coumaryl-CoA. This reaction is catalysed by the enzyme chalcone synthase (CHS). The product of this reaction, 2′,4,4′,6′, tetrahydroxy-chalcone, is normally rapidly isomerized by the enzyme chalcone flavanone isomerase (CHI) to produce naringenin. Naringenin is subsequently hydroxylated at the 3 position of the central ring by flavanone 3-hydroxylase (F3H) to produce dihydrokaempferol (DHK).
The B-ring of DHK can be hydroxylated at either the 3′, or both the 3′ and 5′ positions, to produce dihydroquercetin (DHQ) and dihydromyricetin (DHM), respectively. The pattern of hydroxylation of the B-ring plays a key role in determining petal color, with DHK generally leading to the production of the brick red pelargonidin-based pigments, DHQ generally leading to the red/pink cyanidin-based pigments and DHM generally leading to the blue/violet delphinidin-based pigments.
The dihydroflavonols (DHK, DHQ and DHM) can also be acted upon by flavonol synthase to produce the flavonols kaempferol, quercetin and myricetin. The flavonols are colorless but act as copigments with the anthocyanins to enhance flower color.
The next step in the pathway, leading to the production of the colored anthocyanins from the dihydroflavonols, involves dihydroflavonol 4-reductase (DFR) with the production of the leucoanthocyanidins. These flavonoid molecules are unstable under normal physiological conditions and glycosylation at the 3-position, through the action of glycosyltransferases, stabilizes the anthocyanidin molecule thus allowing accumulation of the anthocyanins. In general, the glycosyltransferases transfer the sugar moieties from UDP sugars and show high specificities for the position of glycosylation and relatively low specificities for the acceptor substrates (Seitz and Hinderer, Anthocyanins. In: Cell Culture and Somatic Cell Genetics of Plants. Constabel, F. and Vasil, I. K. (eds.), Academic Press, New York, USA, 5: 49-76, 1988). Anthocyanins can occur as 3-monosides, 3-biosides and 3-triosides as well as 3,5-diglycosides and 3,7-diglycosides associated with the sugars glucose, galactose, rhamnose, arabinose and xylose (Strack and Wray, In: The Flavonoids—Advances in Research since 1986. Harborne, J. B. (ed), Chapman and Hall, London, UK, 1-22, 1993).
Glycosyltransferases involved in the stabilization of the anthocyanidin molecule include UDP glucose:flavonoid 3-glucosyltransferase (3GT), which transfers a glucose moiety from UDP glucose to the 3-O-position of the anthocyanidin molecule to produce anthocyanidin 3-O-glucoside.
In petunia and pansy (amongst others), these anthocyanins can then be glycosylated by another glycosyltransferase, UDP rhamnose:anthocyanidin 3-glucoside rhamnosyltransferase (3RT), which adds a rhamnose group to the 3-O-bound glucose of the anthocyanin molecule to produce the anthocyanidin 3-rutinosides, and once acylated, can be further modified by UDP: glucose anthocyanin 5 glucosyltransferase (5GT).
Many anthocyanidin glycosides exist in the form of polyacylated derivatives. Acylation may be important for uptake of anthocyanins into the vacuoles as was demonstrated by Hopp and Seitz (Planta 170: 74-85, 1987). The acyl groups that modify the anthocyanidin glycosides can be divided into two major classes based upon their structure. The aliphatic acyl groups include malonic acid or succinic acid and the aromatic class includes the hydroxy cinnamic acids such as p-coumaric acid, caffeic acid and ferulic acid and the benzoic acids such as p-hydroxybenzoic acid.
Acylation of the anthocyanidin 3-rutinosides with either p-coumaric acid or caffeic acid (Griesbach et al., Phytochemistry 30: 1729-1731, 1991) occurs in Petunia hybrida. In other plant systems, acylation of flavonoids by aliphatic acids, such as malonic acid, succinic acid and acetic acid also occur (Goto, Tetrahedron 27: 2413-2416, 1987; Stafford, Flavonoid Metabolism. CRC Press, Inc. Boca Raton, Fla., USA, 1990).
Methylation at the 3′ and 3′, 5′ positions of the B-ring of anthocyanidin 3-(p-coumaryl)rutinoside-5-glucosides occurs in petunia. It has been demonstrated in cell-free extract of flower buds of P. hybrida that S-adenosyl-L-methionine is the methyl donor and O-methyltransferase acts on anthocyanidin 3(p-coumaryl)rutinoside-5-glucoside. Under the conditions used, no methylating activity was detected when anthocyanidins, anthocyanidin 3-glucosides, anthocyanidin 3-rutinosides, caffeic acid or p-coumaric acid were used as substrates (Jonsson et al., Phytochemistry 21(10): 2457-2460, 1982).
Methylation of the B ring of anthocyanins is controlled by the Mt1, Mt2, Mf1 and Mf2 loci in petunia (Jonsson et al., Theor. Appl. Genet. 68: 459-466, 1984b). The four enzymes thought to be encoded by each gene have been described. They catalyze both 3′ and 5′ O-methylation of the B ring. The 3′5′ methylation activity is more pronounced with the Mf1 and Mf2 encoded enzymes (Jonsson et al., 1984b, supra).
The Mt loci were thought to encode S-adenosyl-L-methionine:anthocyanin 3′-O-methyltransferase (3′FMT) and the Mf loci to encode S-adenosyl-L-methionine:anthocyanin 3′,5′-O-methyltransferase activity (3′5′FMT) and that the enzymes only methylate the anthocyanin 3-(p-coumaryl)rutinoside-5-glucoside. (Jonsson et al., 1982 supra; Jonsson et al., Planta 160: 174-179, 1984a; Jonsson et al., 1984b, supra). It was originally thought that the genes Mf1 and Mf2 could only express themselves if at least one of the genes Mt1 or Mt2 is represented by its dominant allele. However, biochemical studies have since contradicted these findings by showing that both enzymes were capable of methylating delphinidin 3-(p-coumaryl)-rutinoside-5-glucosides to the corresponding malvidin pigment in in vitro assays (Jonsson et al., Theor. Appl. Genet. 66: 349-355, 1983). Furthermore, the action of Mf1 and Mf2 was thought to be restricted to the corolla limb (Wiering, Hort. Genen. Phaenen. 17: 117-134, 1974).
The presence of methylated anthocyanin pigments have been reported in Petunia sp. (Sink (ed), Petunia, Springer-Verlag, Berlin, 1984; Ando et al., Biochemical systematics and ecology, 27: 623-650, 1999), Plumbago sp. (inter alia, Harborne, Phytochemistry, 6: 1415-1428, 1967; Harborne, Arch Biochem Biophys, 96: 171-178, 1962), Vitis sp. (Cachio et al., American J of Ecology and Viticulture, 43: 244-248, 1992), Babiana stricta (Toki et al., Phytochemistry, 37: 885-88-7, 1994), Pinus sp. (Andersen, Biochemical systematics and ecology, 20: 145-148, 1992), Picea sp., Larix sp., Phaseolus sp. (Hungria et al., Plant Physiology, 97: 751-758, 1991; Takeoka et al., Journal of Agricultural and Food Chemistry, 45: 3395-3400, 1997), Solanum sp. (Lewis et al., J. of the Science of Food and Agriculture, 77: 45-57, 1998), Vaccinium sp. (Ballington et al., Can. J. of Plant Sci., 68: 241-246, 1988; Skrede et al., J of Food Science, 65: 357-364, 2000), Cyclamen sp. (Webby and Boase, Phytochemistry, 52: 939-941, 1999), Iris sp. (Yabuya et al., Euphytica, 98: 163-167, 1997; Yabuya and Noda, Euphytica, 103: 325-328, 1998), Pelargonium sp. (Mitchell et al., Phytochemistry, 47: 355-361, 1998; Kobayashi et al., Breeding Science, 48: 169-176, 1998), Geranium sp. (Andersen et al., Phytochemistry, 38: 1513-1517, 1995), Pisum sp. (Crowden, Phytochemistry, 21: 2989-2990, 1982), Lathyrus sp. (Rat'kin et al., Zh Obshch Biol, 41: 685-699, 1980), Clitoria sp (Srivastava and Pande, Planta Med, 32: 138-140, 1977), Catharanthus sp. (Carew and Krueger, Phytochemistry, 15: 442, 1976), Malvia sp. (Takeda et al., Phytochemistry, 28: 499-500, 1989), Mucuna sp. (Ishikura and Shibata, Bot Mag (Tokyo), 86: 1-4, 1973), Vicia sp. (Catalano et al., J. Agricultural and Food Chemistry, 49: 4568-4570, 1998; Nozzolillo et al., Canadian Journal of Botany, 67: 1600-1604, 1989), Saintpaulia sp. (Griesbach, Phytochemistry, 48: 829-830, 1998), Lagerstroemia sp. (Toki and Katsuyama, J. Jap Soc Hortic. Sci., 63: 853-861, 1995), Tibouchina sp. (Francis et al., J Am Soc Hortic Sci, 107: 789-791, 1982, Terahara et al., J. Natural Products, 56: 335-340, 1993), Hypocalyptus sp. (Van Wyk et al., Biochemical systematics and ecology, 23: 295-297, 1995), Rhododendron sp., Linum sp., Macroptilium sp. (Imrie and Hutton, J. Hered., 69: 54-56 1978), Hibiscus sp. (Kim et al., Phytochemistry, 28: 1503-1506, 1989; Kim and Fujieda, J. Kor. Soc. Hortic. Sci., 32: 247-255, 1991), Hydrangea sp. (Takeda et al., Phytochemistry, 29: 1089-1091, 1990), Ipomoea sp. (Saito et al., Phytochemistry 41: 1607-1611, 1996), Cymbidium sp. (Woltering and Somhorst, J. Plant Physiol., 136: 295-299, 1990), Millettia sp. (Parvez and Ogbeide, Phytochemistry, 29: 2043-2044, 1990), Hedysarum sp. (Chriki and Harborne, Phytochemistry, 22: 2322-2323, 1983; Chriki, Agronomie, 10: 553-540, 1990), Lespedeza sp., Antigonon sp. (Tiwari and Minocha, Vijnana Parishad Anusandhan Patrika, 23: 305-308, 1980) and Pisum sp. (Crowden, Phytochemistry, 21: 2989-2990, 1982).
This list describes the species from which methylated anthocyanin pigments have been reported. However, it is expected that these pigments will be present in many other species.
Plant S-adenosyl-L-methionine-dependent O-methyltransferases (SAM-OMTs) are key enzymes in metabolic pathways such as phenylpropanoid and flavonoid synthesis. These enzymes facilitate the transfer of the methyl group of S-adenosyl-L-methionine (SAM) to the hydroxyl group of an acceptor molecule with the formation of its methyl ether derivative and S-adenosyl-L-homocysteine as products. The chemical mechanisms of methyl transfer reactions are identical. However, SAM-OMTs differ in their selectivity with respect to the stereochemistry of the methyl acceptor molecules, as well as the substitution pattern of their phenolic hydroxyl groups. Methylation of different substrates is generally catalysed by distinct SAM-OMTs. However, some enzymes have a broad substrate range although they will usually have a preference for a specific substrate or group of compounds.
Currently, there are over 87 plant-derived sequences encoding SAM-OMTs in the GenBank database. Practically all of these sequences contain three highly conserved consensus motifs (motifs A, B and C) exhibiting a specific spatial arrangement (Joshi and Chiang, Plant Mol. Biol. 37: 663-674, 1998; Ibrahim and Muzac, In Recent advances of phytochemistry. Evolution of metabolic pathways. Elsevier Science Ltd. 34: 349-385, 2000). Since these motifs are present in most plant SAM-OMTs regardless of substrate specificity, it is thought that they are essential for SAM binding.
By considering the length of the encoded protein and the spatial relationships between motifs A and B and motifs B and C, the plant SAM-OMTs can be grouped into two distinct classes. Group I contains all the CCoAOMTs (caffeoyl-CoA SAM-OMTs) and exhibits a specific spatial arrangement of 19 amino acids between motifs A and B, and 24 amino acids between motifs B and C. Group II contains proteins with a distance of 52 residues between motifs A and B and 30 residues between B and C. Group II SAM-OMTs include COMTs (caffeic acid OMTs), F3′OMT (flavonoid 3′-OMT) (Gauthier et al., Plant Mol. Biol. 32: 1163-1169, 1996), IOMTs (isoflavone OMTs) (He and Dixon, Plant Mol. Biol. 36: 43-54, 1998), 2′OMTs (isoliquiritigenin 2′-OMT) (Maxwell, Plant J. 4(6): 971-981, 1993), IMT (inositol OMT) (Rammesmeyer et al., Arch. Biochem. Biophys. 322(1): 183-188, 1995), and F7OMT (flavonoid 7-OMT) (Christensen et al., Plant Mol. Biol. 36: 219-227, 1998), among others. It is important to note at this point that those enzymes for which substrate analysis has been undertaken and for which function has been assigned are usually tested with a limited range of substrates. The flavonoid SAM-OMT sequences that have been isolated to date have all been implicated in defense responses with none being shown to have activity on anthocyanins and belong to the Group II SAM-OMTs.
CCoAOMT proteins, or Group I SAM-OMTs, vary in length between 231-248 amino acids and usually require divalent cations, such as Mg2+, for catalytic activity. Group II SAM-OMTs are generally around 344-383 amino acids in length and do not require divalent cations. The two groups share approximately 20-30% amino acid identity.
In addition to the above modifications, pH and copigmentation with other flavonoids such as flavonols and flavones can affect petal color. Flavonols and flavones can also be aromatically acylated (Brouillard and Dangles, In: The Flavonoids—Advances in Research since 1986. Harborne, J. B. (ed), Chapman and Hall, London, UK, 1-22, 1993).
The ability to control the activity of flavonoid methyltransferases (herein after referred to as “FMT”) specifically anthocyanin methyltransferases would provide a means of manipulating petal color thereby enabling a single species to express a broader spectrum of flower colors. Such control may be by modulating the level of production of an indigenous enzyme or by introducing a non-indigenous enzyme.